A stent is an elongated device used to support an intraluminal wall. In the case of stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft.
A prosthesis may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, a prosthesis is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the prosthesis, maintained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been advanced into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the prosthesis to be deployed from the surrounding sheath or catheter in which it is maintained (or alternatively the surrounding sheath or catheter is retracted from the prosthesis), whereupon the prosthesis expands to a predetermined diameter at the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of stent architectures are known in the art, including many that comprise multiple regions, each region having a different stiffness, radial strength, and/or kink resistance. For example, referring now to FIG. 1, one configuration of a bifurcated modular stent 10 adapted to treat abdominal aortic aneurysms (AAA) comprises two components: a bifurcated component 12 comprising a trunk section 14 with an attached or unibody fixed ipsilateral iliac leg (IIL) 16 and a socket 18, and a second component 20 that comprises the adjoining contralateral iliac leg (CIL). When CIL 20 is connected into socket 18 as shown in FIG. 1, interface section 19 between the CIL and the socket is stiffer than interface section 15 between IIL 16 and trunk section 14. The mismatched stiffness between interfaces 15 and 19 arises in part because interface 19 comprises an overlap between the structure of leg 20 and the structure of socket 18, whereas interface 15 has no such overlapping structure.
The resulting different properties of interfaces 15 and 19 may predispose the stent to unwanted in vivo behavior such as local kinking, occlusion, or bending. Because the lumen itself into which stent 10 is placed may vary in stiffness and/or geometry, may require the stent to conform to tortuous anatomy, and/or may require the stent to accommodate bending or longitudinal or transverse deformations, it is desirable that the stent mimic the lumen and respond coherently to applied deformation or loading. Thus, it is desirable to provide a stent design that does not have local regions of mismatched stiffness such as interfaces 15 and 19 as shown in FIG. 1.
The interfaces between adjacent stent regions of different stiffness may also cause kinking, occlusion, or bending at the interface due to the drastic change in properties from one region to another. Thus, it is also desirable to minimize problems caused by abrupt stiffness interfaces between adjacent stent regions.